Ruby head canary test coverage

[arielvalentin]

The setup-ruby action seems to support installing Ruby head, which I presume means we are able to work off the latest development version pulled from GitHub.

https://github.com/ruby/setup-ruby/blob/6bd3d993c602f6b675728ebaecb2b569ff86e99b/ruby-builder-versions.json#L16C6-L16C10

Adding test coverage for head will allow us to prepare for future unexpected issues and incompatibility but should not prevent us from releasing.

[dmathieu]

If the test suite runs for head on every PR, an unrelated failure would break every CI run.
It feels like this should run at regular intervals (weekly?) and open an issue if there's a failure.

[arielvalentin]

@dmathieu I should have been more explicit but that is what I mean by making a canary build as opposed to having it run on CI every time a PR is opened or merged:

Adding test coverage for head will allow us to prepare for future unexpected issues and incompatibility but should not prevent us from releasing.